it's not readdir() that is slow - it's the way ls needs to load the whole directory into memory then do a bunch of things on it (sorting, calculating column siz

it's not readdir() that is slow - it's the way ls needs to load the whole directory into memory then do a bunch of things on it (sorting, calculating column sizes, etc), and depending on what you have in your defaults or passed options it might also try to stat() every of those files first.